Optical communication glass fibers are made from glass such as quartz glass and are extremely small in diameter, for which reason they are weak in strength. In order to make up such weakness in strength of optical communication glass fibers and to avoid strain on their surfaces, generally a primary coat is applied onto the surface of those fibers using, for example, nylon, polyethylene, polyurethane, epoxy resin, or silicone resin.
As shown on page 12 of Japanese Patent Laying Open Print No. 100734/76, it is preferable that such primary coat materials have a higher refractive index than that of the clad layer of optical communication glass fibers.
Among those materials, moreover, silicone resin having a higher refractive index than that of the clad layer is considered to be the most preferred material for improving the characteristics of optical communication glass fibers, as is described in Japanese Patent Laying Open Print No. 150050/77.
However, the silicone resin which has heretofore been used in this kind of application is disadvantageous in that the cured film is very hard, that the air bubbles incorporated before or during the coating operation are difficult to be removed, that the components of the composition are less compatible with each other resulting in the curing being slowed down, and that the coated film surface becomes rough.
It is an object of this invention to remedy such disadvantages associated with conventional primary coat materials.
It is another object of this invention to provide a coating material for optical communication glass fibers, characteristic in that the incorporated air bubbles are easy to be removed, that it can be applied easily onto an optical communication glass fiber having a clad layer, that it can be cured quickly, that the adhesion thereof to such glass fiber is satisfactory, and that it can form a smooth film rich in flexibility.
It is a further object of this invention to provide an optical communication glass fiber coated with a coating material having the above-mentioned characteristics.